Transistor radio receiver tuning indicator



May 27, 1958 T. M. sco'rT ET AL TRANSISTOR RADO RECEIVER TUNING-INDICATOR Filed Aug. 17, 195e -Illll- Nw @v NWN United States TRANSISTOR RADIO RECEIVER TUNEIG lNDlCATOR Application August 17, 1956, Serial No. 604,733

7 Claims. (l. 25-2l) This invention relates to radio signal receiving systems, and in particular to such systems in which transistors are utilized as active signal amplifying devices.V

One of the advantages obtained by the use of transistors in radio signal receiving systems is that the power drain from the supply source is reduced. Most radio signal receiving systems are provided with a dial lamp which illuminates the turing dial of the receiver. in the conventional type receiver the dial lamp is illuminated when the receiver is turned on and remains illuminated as long as the receiver is in the on condition. in signal receiving systems employing transistors, however, the dial lamp may account for more than half of the no-signal current drain from the supply source, thus counteracting to a substantial degree the small power drain realized by the use of the transistors.

It is accordingly an object of this invention to provide improved means in a transistorized radio signal receiver for illuminating the tuning dial thereof and for reducing the average power drain of the receiver.

Because of cost considerations, most radio signal receiversV are not provided with means for visually indicating the tuning of the receiver. It is desirable, however, to provide a receiver with means for accomplishing this function.

it is, therefore, another object of this invention to provide improved circuit means for illuminating the tuning dial of a radio signal receiving system with a minimum amount of power drain and for providing a visual indication of the tuning of the receiver.

The tuning dial lamp of a radio receiver, in accordance with the invention, is illuminated when the receiver is not tuned into a received signal. When the receiver is tuned to an incoming signal, however, the dial light is turned ot in response to the automatic gain control (AGC) current of the receiver. Since the receiver` is normally tuned to an incoming signal, the dial lamp is normally not illuminated, thus reducing the average power drain. In addition, a visual indication of the tuning is provided as the dial lamp is extinguished. This type operation is achieved, in accordance with the invention, by connecting the tuning dial lamp in the output circuit of an auxiliary transistor which may be referred to as the dimmer transistor. This transistor is connected with the output circuit of one of the transistor ampliers of the receiver to'which the AGC current is. applied. The conductivity of the transistor amplifier may be oposite to that of the dimmer transistor. When the receiver is not tuned to an incoming signal,.the dial lamp is il# luminated by Output current ow from the dimmer transistor. When the receiver is tuned to an incoming signal, however, AGC current is applied to the transistor amplier to reduce its output current which in turn reduces the output current of the dimmer transistor to extinguish the dial lamp.

The novel features that are considered characteristic of this invention are set forth with particularity in the arent ricc appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing, in which the single iigure is a schematic circuit diagram, partially in block diagram form, of a radio signal receiving system embodying the invention.

Referring now to the drawing, a superheterodyne signal receiving system includes, as is conventional, an antenna 8, a radio frequency amplifier 10, and a tuner and converter 12, having a tuned output circuit 14. Signals appearing in the output circuit 14 of the tuner and converter l2 are applied through a secondary winding i6, to the base 24 of a transistor I. F. amplifier 18 which is connected to operate in the common emitter configuration. The transistor 13 may be considered to be of the P-NP junction type and includes, in addition to the base electrode 24, an emitter Ztl and a collector electrode 22.

The emitter 2G of thertransistor 18 is connected through a negative feedback current stabilizing resistor 26 to ground or reference potential point for the receiver circuit. Pi'he resistor 26 is by-passed for signal currents by a capacitor 28. Output signals from the transistor are derived from the collector 22, or from between the collector 22 and the emitter 20. To this end, the collector 22 is connected to an intermediate point of an inductive winding 3i? of a tuned output circuit 32, which also includes a tuning capacitor 33. To supply negative biasing potentials to the collector 22, it is connected through the lower half of the output winding 3i) to a negative terminal 31 of suitable Vdirect-current supply means such as, for example, a battery (not shown). The intermediate frequency output signals are coupled through a secondary winding 3d, which is in inductive coupling relation with the output winding 30, to the input circuit of a second intermediate frequency signal amplier 35. The output circuit of the second intermediate-frequency amplifier 35 is connected to the input circuit of a signal detector 36. The detector 36 may be, for example, a transistor or a crystal diode and is operative to provide an AGC signal, which may be either as current or voltage, and which is applied through the load 3S to, for example, the emitter 20 of the I. F. transistor ampiier i8. The derived AGC signal may be applied in any well known manner to the transistor 18 to control its The detected audio frequency signal is conveyed from the output circuit of the detector 36 to an audio frequency amplier 49, as indicated by the circuit connection 39, which drives a suitable loudspeaker 42.

To provide illumination of the dial light of the receiver and a visual tuning indication, in accordance with the invention, the collector 22 of the transistor 18 is connected through the upper half of the output winding 30 to the base Sil of an auxiliary or dial lamp dimmer transistor 44. The dhnmer transistor 44 is of an opposite conductivity type to the l. F. transistor amplifier 18 and may be considered to be of the N-P-N junction type. it includes, in addition to the base 50, an emitter 46 and a collector d8. A signal frequency by-pass capacitor 52 is connected from the base electrode 50 to ground which decouples the collector circuit from the common supply. To provide biasing potentials for the transistor 44 the emitter lo is connected to a suitable negative direct-current biasing supply source. To complete the circuit, in accordance with the invention, a dial lamp 54 which may be of the incandescent type is connected between the collector electrode 48 of the dimmer transistor 44 and ground, as shown. The tuning knob and dial are indicated as being located adjacent the indicator lamp 54.

' 1S of P 'type conductivity'and the transistor-44 of N type conductivity, as long as thel polarity ortthe appropriate bias supply source is also reversedl In operation, it will beassitmed initiallyithat'the receiver` is not `turnedto an 'incoming'signalt Inthe absence of signal'input to the receiver,Y there. is Vno AGCJ current. lIn this condition, the direct Vcollector current'oithe transistor 18 will nor- Vrnallylbe"approximately one milliampere; Y' This Vone milliampere of current ows into the base electrode Yt) of the Vdimmertransistor 44 to provide Yamplified direct current flow" equal to the product of the collector current ow of Y transistor 18 fand the current gain, asdefined by the ratio of Ycollector current to' base current 'of the dimmer transistor 44. If`this current gain is equal to vsixty (60) for example, YV,and the collector currentV of the transistor 18 is one milliatnpere,vr 60 milliamperes of collector current Will ow'into the collector 48 of the dimmertransistor ti4and-through the dial lamp 54.- This current flow is suti'icie'nttoY fully energize the'lamp Which,-therefore, is normally illuminated or on in the absence ofan incoming signal H When the receiver` is tuned to an incoming signal, hovv-Y ever, the received signal will be amplified and applied to the' detector 36., AWhichprovides Van YAGC current in accordance with variations inthe amplitude of the received signal,. the AGC Ycurrent increasingwithincreases in the amplitude `ofthe signal -which is applied to the detectorv 36. ThisAGCcurrent gisapplied to the emitter 20 ofY the LF. Vtransistor ampliiier'ls in the `present example,YV

land Yliows in a direction to reduce Vthe emitter current flow ofY transistor.V Accordingly, as the signalk strength and AGC current increase, the gain of the transistor 18 is reduced. ,This greatly-reduces the-"directV collector alsoV serves Vto direct collector current variation amplifier, means connecting said tuning indicator'lamp with the collector of said auxiliary transistor to illuminate t said lamp in response to collector current ilowtof saidV auxiliary transistor in the absence of an applied signal, and means connecting said automatic gain control means with said transistor ampliier to reduce the gain and the direct collector currentthereof and the direct collector current of said auxiliary transistor to extinguish said dial lamp in the presence of an applied signal. ,k

2. in a radio signal receiving system including a tuning indicator lamp, the combination Vcomprising automatic gain control means adapted to Yprovide automatic gain control of said receiving system in response to applied signals, a transistor signal ampliiier o f one conductivity type having a base, an emitter, and a collector electrode,

a lamp dimmer transistor of an opposite conductivityV type havinga base, an emitter, anda Vcollector electrode, direct-current conductive means connecting the collector electrode of said transistor. signal amplifier with the base electrode of said dimmer transistor to vary the collector current flow of said dimmer transistor .in response to collector current variation of said transistor amplifier,

means connectingV said tuning indicator lamp with .the collector of said dimmer transistor -to illuminate said lamp in response Vtocollector current flow of said dimmer transistorin the absence of an applied signal, and means connecting said automatic gain control means with said transistor amplifier to reducefthe gain andrthe direct eollector current thereof vand' Vthe vdirect collector current of Y said dimmer. transistor to extinguish said lindicatorlamp Y and provide visual tuning indicationfor said receiver in the presenee of anV applied signal.v y

3. In a radio signalreceiving system, they combination Y' with a tuningdial anda tuning dial lamp for illuminating saidY dial, of signal. detection Ameans' for providing an automatic gain control current inresponse to 'an appliedVY s signal, a transistor signalampliiier of'one conductivity;Y VtypeV havinga baseyan emitter, and :a collector electrode, Y

a signalinput circuit connected with said base electrode,

. a signal output circuit connected Withsaid collector eleccurrent Vflowrofthe transistorlS, which current orv'vs i into Ythe base of the dimmer transistor 44; Thus the collector current owof Vthe dimmer Ytransistor 44`is reduced to one milliampere and Will Vgenerally be less Vthan one milliampere. This current isrinsucient to maintain the latnptintthe illuminated ,or` ,on condition so that when the receiver is tuned `to an applied input signal the lamp` 54 will be extinguished. Since the receiver is normally Vtuned to the incoming signal, the average dial lamp Y power .drain is greatly reduced yet the lamp is lighted when it is .normally Vu,sed,t ha,t,is when the ,receiver is being 'Y tuned. In addition, Vsince the'dial lamp -isV operated inter- VrnittentlyhitV may be possible toY use more than its rated continuans-'duty` current, resulting Yin greater luminous "efficiency Moreover, sincevrthe' lamp is yextinguished when the signal which isapplied tothe detector 36 increasesk in amplitude ,the extinguishing of-the lamp V54 provides a positiver'indication of the tuning function. Thus by using lone extra'transistorV and relatively simple circuitrconne'ctions, in accordance Ywith the.' invention,

theraveragepowerdrainrof the receiver is reduced and a visual tuning indication is provided.

Whatis claimed is:

Vlgjln a signal receiving Ysysterrnthe combination with 'rartuning' indicator lamp, automatic gain control means adaptedvto provide anautomatic gain control signalein Yr'eslgaonsejtoanapplied signal, anda transistor signal amplifier having a base, an emitter, and acollector elecand a' collectorY electrode, meansv connecting -the collector electroderof said transistor ampliner-With the base elec-V Vtrode of saidauxiliary transistor to vary the direct collec- Vtoi' current iioWofY said auxiliary transistorfin response Y electrode, means providing a direct current supply source Y connected Vwith theccollector electrode of saidrtransistor Y amplifier and-the emitter eletcrode of said dimmer trant sistor forapplying biasing potentials thereto, VVdirect-,cur- Y rent conductive means'connecting the collector electrode Y of .said transistor ampliiierwith the base electrode YofY said dimmer transistorto rvarythe collector current -flow of .said dimmer AtransistorIin response to YcollectorcurrentV va'riationror said transistor a`mplier,-direct-currentrcontrode, a dial lamp dimmer ltransistor ofan opposite conductivity typeV having aV base, an-'emitter and a'collector Vductiverneans connecting said ktuning dial lamp between thecollector ofsaid dimmer transistor and atpoint of reference Ipotential insaid system to illuminate said lamp v in response to collector4 current ilow of said dimmer tran sistor in the-absence'ot an ,applied signal, and means connecting'said signal detection lmeans with the emitterY electrode ofV said transistor'amplitier'to reduce the gain and the Vdirectcollector: current thereof and .the directY collectorcurrent -of said dimmer transistor to extinguishY said dial lamp and provide visual tuninggindication for said receiver in the presencel offan appliedrsignall` Ytr'ode,f an auxiliary transistor having abase,anemitter,`

' 4. A radio signal receiving system as defined in clairn 3 Y wherein said'transistor.` signal ampliieraisja junction transistor oftheP-N-fltype, said dimmertransistor is a1 junction transistor" of the N-P-N.type, and saidrdirect current supply source is of negative polarity,y p p Y g 5.n In a signal Yreceiving system in luding av'tuningindicator lamp, the'coinbination-with automaticrgain control means for providing automaticrgain control of said system in response to applied signals, atransistor ,signal ampli-VV v lier, and means providing a signaloutput .circuitV con' nected with said transistor amplifier, of an auxiliarytransistor, 1 direct-current Aconductive* means connecting said of said transistor iitput circuit with said auxiliary transistor to vary the current ow of said auxiliary transistor in response to output current variation of said transistor amplier, means Connecting said tuning indicator lamp with said auxiliary transistor to illuminate said lamp in response to current ow of said auxiliary transistor in the absence of an applied signal, and means connecting said automatic gain control means with said transistor amplifier to reduce the gain and the output current thereof and current of said auxiliary transistor to extinguish said dial lamp in the presence of an applied signal.

6. A tunable signal translating system comprising, in combination, a tuning indicator lamp, at least one signal translating stage including a transistor signal amplifier having base, emitter, and collector electrodes, an auxiliary dimmer transistor having base, emitter, and collector electrodes, means providing automatic gain control of said system responsive to applied signals, means connecting said automatic gain control means with said transistor amplier to control the gain and the collector current thereof inversely relative to the strength of an applied 6 alternating current signal, means connecting said indicator lamp in circuit with the collector of said dimmer transistor to illuminate said lampin the absence of an applied signal, and means connecting the collector of said transistor ampliter with the base of said dimmer transistor to control the collector current of said dimmer transistor inversely relative to the strength of an applied alternating current signal to eti'ectively extinguish said lamp in the presence of an applied alternating current signal.

7. A signal receiving system as defined in claim 6 wherein said transistors are of opposite conductivity types.

References Cited in the file of this patent UNITED STATES PATENTS 1,887,329 Schade Nov. 8, 1932 2,125,468 Sinninger Aug. 2, 1938 2,514,327 Grant July 4, 1950 2,663,800 Herzog Dec. 22, 1953 2,666,818 Shockley Jan. 19, 1954 

